Pyrotechnic actuator with a cylinder having communicating chambers

ABSTRACT

A pyrotechnic actuator for an active bonnet is provided that includes, but is not limited to a cylinder, a piston which can be displaced in the cylinder under the influence of a propellant gas and a first gas generator for producing the propellant gas. The actuator includes, but is not limited to at least one further gas generator, which can be ignited independently of the first gas generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National-Stage entry under 35 U.S.C. §371based on International Application No. PCT/EP2006/009540, filed Oct. 2,2006, which was published under PCT Article 21(2) and which claimspriority to German Application No. DE 10 2005 051 657.2, filed Oct. 28,2005, which are herein incorporated in their entirety by reference.

TECHNICAL FIELD

The present invention relates to a pyrotechnic actuator for an activebonnet of a motor vehicle.

BACKGROUND

An active bonnet is taken to mean a bonnet which is automatically raisedin the event of an accident by one or more actuators to increase thespacing between the bonnet and parts of the motor vehicle which arelocated therebelow and are difficult to deform, and to thus provide apedestrian possibly impacting against the bonnet with an extendedbraking path. This is intended to avoid the pedestrian colliding againstthe non-deformable body parts at a speed which may lead tolife-threatening injuries.

Various pyrotechnic actuators have already been proposed for thispurpose which use gas generators, such as are also known from airbags,to drive the bonnet movement. These pyrotechnic actuators have anadvantageously short response time as they are generally electricallyignited and therefore solid parts do not have to be accelerated in atime-consuming manner to activate them, and they achieve a powerfulacceleration of the bonnet so it reaches its raised position in theshortest time. However, it is disadvantageous that the conventionalpyrotechnic actuators are not reversible. In other words, they are onlysuitable for a single use and then have to be exchanged. A faultytriggering of the actuators therefore makes an expensive stay in aworkshop necessary every time. As it is hardly possible to avoidtriggering of the actuators in the event of an accident, if the bonnetis unaffected by the events of the accident, the cost of repair of avehicle equipped with pyrotechnic actuators is generally higher after anaccident than those of a vehicle without these actuators.

A reversible actuator for a motor vehicle is known from DE 103 08140 B3,which is driven mechanically by spring force. An actuator of this typemakes it apparently simple, after it has been triggered, to bring thebonnet back into its normal position from which a renewed triggering cantake place, but the spring has to have large dimensions because of thevery short lifting times so reversal of the spring is possible only withthe aid of a gearing down mechanism. A further problem emerges from thefact that the tensioned springs press with a high force against anobstacle which, on activation of the actuator has to be moved extremelyrapidly. A high pressure of the spring against the obstacle makes acorrespondingly high driving force to remove the obstacle necessary, thebuild up of which severely delays the actuating movement of theactuator.

A further problem of conventional active bonnets is that the knownactuators are in a position to sharply accelerate the bonnet but, assoon as the actuators reach their stop, the bonnet is decelerated stillmore abruptly than it was previously accelerated, and made to stronglyvibrate. If a pedestrian impacts against a region of the bonnet betweentwo actuators while said region is deflected downward, the spacingbetween this region of the bonnet and hard parts of the vehicle locatedbelow is sharply reduced, and there is a risk that the distanceavailable for the deceleration of the pedestrian is not sufficient toavoid a collision against these hard vehicle parts.

In view of the foregoing, at least one object of the present inventionis to provide an actuator for an active bonnet which is suitable fordriving a plurality of lifting movements of the bonnet without making astay in a workshop necessary after each of these lifting movements, andwhich thus avoids the disadvantages of a mechanical drive. In addition,other objects, desirable features, and characteristics will becomeapparent from the subsequent summary, detailed description, and theappended claims, taken in conjunction with the accompanying drawings andthis background.

SUMMARY

The at least one object, desirable features and characteristics, areachieved by a pyrotechnic actuator with a cylinder, a piston which canbe displaced in the cylinder under the influence of a propellant gas anda plurality of gas generators which can be ignited independently of oneanother.

The actuator preferably also has an electronic ignition circuit, which,upon external ignition commands, ignites the gas generators in each caseindividually and sequentially.

A further object of the invention is to provide an actuator which is ina position once the bonnet has been lifted to prevent or at least limitundesired vibrations thereof.

This object is achieved in that, in a pyrotechnic actuator with acylinder, a piston which can be displaced in the cylinder under theinfluence of a propellant gas and a first gas generator for producingthe propellant gas, the cylinder has two chambers on either side of thepiston, which can be charged with propellant gas from the gas generator.If, in a normal position of the actuator, the first of these chambers issignificantly smaller than the second, a small quantity of gas fed intothe first chamber is sufficient to build up a high pressure therein,which drives the movement of the piston. This movement inevitablycontinuously reduces the volume of the second chamber, so acounter-pressure building up in this second chamber graduallydecelerates the movement of the piston and, with it, the movement of abonnet driven by the actuator. A hard stopping of the piston at the endof this adjustment path that would excite strong vibrations of thebonnet is thus avoided.

In order to avoid an unnecessarily early build up of a counter-pressurein the second chamber, the second chamber can preferably be charged withthe propellant gas after the first chamber. A sequence of this type canbe structurally ensured in a simple manner in that the second chambercan be charged with the propellant gas through the first chamber. Withan arrangement of this type, the second chamber only receives propellantgas to a significant extent when the latter has built up sufficientpressure in the first chamber, in order to penetrate from there into thesecond chamber.

In order to delay the supply of the second chamber with propellant gas,an inlet passage for propellant gas into the second chamber ispreferably blocked in a rest position of the piston and is only openwhen the piston is deflected from the rest position.

In order to ensure an effective support of the bonnet in the raisedstate by the gas pressure prevailing in the first chamber of theactuator, the inlet passage should expediently also be blocked when thepiston is in an end position opposite to the rest position.

A throttled transfer of propellant gas from the first chamber into thesecond can be implemented in a simple manner if the inside width of thecylinder in a central region of the cylinder is greater than in at leastone of its end regions.

If a pedestrian impacts against the bonnet this will generally lead tothe actuator piston moving back, during which movement work is carriedout against the pressure of the propellant gas in the first chamber, sothe pedestrian is decelerated. In order to keep the pressure of thepropellant gas in the first chamber during this downward movement, thepiston expediently comprises a central piece connected to a piston rodand an apron surrounding the central piece and axially displaceablethereon.

The axial displaceability of the apron against the central piece shouldbe limited in both directions by stops to ensure that the apron followsa movement of the central piece.

To facilitate the gas transfer into the second chamber during the upwardmovement of the bonnet, the apron may be provided with local throughopenings.

The spacing of the through openings from one end of the apron ispreferably larger than the length of the central region to ensure that atransfer of propellant gas from the first chamber into the secondchamber substantially only takes place during an upward movement of thebonnet, but not during a downward movement.

A throttle point, by means of which the second chamber communicates withthe surroundings, prevents a counter-pressure decelerating the pistonmovement from building up earlier than necessary in the second chamber.

The embodiments of the invention also relates to a motor vehicle with anactive bonnet which is held on a frame of the motor vehicle by means ofactuators of the type defined above. As the actuators themselves canyield in each case upon an impact, a bonnet held by them may be flexibleover its entire surface, so a pedestrian is effectively protectedregardless of on which location of the bonnet he impacts.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 shows a motor vehicle with a bonnet held by actuators in a raisedposition;

FIG. 2 shows a perspective exploded view of an actuator according to theinvention;

FIG. 3 shows a schematic section through an actuator cylinder accordingto the present invention in the normal position;

FIG. 4 shows the actuator cylinder from FIG. 3 with a raised piston;

FIG. 5 shows a schematic section through an actuator cylinder accordingto a second configuration of the invention in the normal position;

FIG. 6 shows an actuator cylinder during the raising of the bonnet;

FIG. 7 shows an actuator cylinder with a maximally raised bonnet;

FIG. 8 shows the actuator cylinder at a first instant during a downwardmovement of the bonnet driven by the impact of a pedestrian; and

FIG. 9 shows a section through the actuator cylinder at a second, laterinstant of the downward movement.

DETAILED DESCRIPTION

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit embodiments of the invention orthe application and uses. Furthermore, there is no intention to be boundby any theory presented in the preceding background or the followingdetailed description.

FIG. 1 schematically shows a motor vehicle with an engine bonnet 1,which is held in a raised position compared to a normal position, inwhich it is flush with adjacent body parts 6, by actuators 5, 3 arrangedadjacent to the front or rear edge of the bonnet 4, 2. The bonnet 1 issupported exclusively by the actuators 3, 5.

FIG. 2 shows a perspective exploded view of one of these actuators 3, 5.It comprises an elongated cylinder 7, which carries two fasteningflanges 8 for the assembly of the cylinder 7 on a rigid frame of themotor vehicle. A gas inlet flange 9 with an inlet opening 10 is arrangedbetween the fastening flanges 8. A gas generator carrier 11 is providedto be fastened in a gas tight manner on the inlet flange 9. The gasgenerator carrier 11 has chambers for three gas generators 12 which areconnected to the inlet opening 10. A destructible partition, not shownin the Figure, may be attached in the gas generator carrier 11 in apassage between each chamber and inlet opening 10, in each case, whichpartition tears open when the gas generator 12 is ignited in the chamberassociated with it, but protects a gas generator 12 accommodated in thechamber associated with it from also being ignited by the explosion of agas generator 12 in an adjacent chamber.

A cover 13 to be assembled on the side of the gas generator carrier 11remote from the cylinder 7 contains an electric ignition circuit which,on receipt of an ignition command by way of a signal cable 14, in eachcase ignites one of the gas generators 12.

The actuator of FIG. 2 is therefore in a position to drive three liftingmovements of the bonnet 1, before it is used up and has to be exchanged.

It is obvious that more or less than three gas generators 12 may also beaccommodated in the gas generator carrier 11. The number of gasgenerators will generally, however, not greater than five or six, as thenumber of the bonnet lifting movements to be expected during the servicelife of a motor vehicle is limited.

Basically, a gas generator carrier with a single gas generator wouldalso be a possibility and would then have to be exchanged each timeafter a lifting of the bonnet 1 while the cylinder itself could remainin the vehicle. An exchange of the generator carrier which would then benecessary after each lifting of the bonnet 1, would, however, requireconsiderable safety precautions which can only be ensured withdifficulty in a motor vehicle workshop.

FIG. 3 shows a schematic section through the cylinder 7 of the actuatoraccording to a first configuration of the invention in the normal state.A displaceable piston 15 divides the interior of the cylinder 7 into twochambers, a lower chamber 16, the volume of which is minimal in thenormal position shown, and an upper chamber 17, which takes up almostthe entire interior of the cylinder 7, and through which a piston rod 18extends, to the upper end of which, not shown, the bonnet 1 is fastened.A gas line 19 extends from the inlet opening 10 into the lower chamber16.

The wall of the cylinder 17 is subdivided in the longitudinal directioninto three portions 20, 21, 22. The cross-section of the lower portion20 and the upper portion 22 corresponds to that of the piston 15, so thelatter, in these portions, substantially rests closely against thecylinder wall. In the central portion 21, the inside width of thecylinder is slightly larger than in the portions 20, 22, so when thepiston 15 has been raised into the section 21 by propellant gas flowinginto the gas chamber 16 by way of the gas line 19, part of thepropellant gas can flow past the piston 15 into the upper chamber 17, asindicated by arrows 23. When the piston 15 reaches the upper portion 22in the course of its further upward movement, it again closely adjoinsthe cylinder wall and the gas in the upper chamber 22 is compressed. Thecounter-pressure resulting therefrom decelerates the piston 15 and, withit, the bonnet 1, so the piston 15 does not, or at most only gently,strikes against the upper wall of the cylinder 7.

In this upper wall, a throttle passage 24 is shown, through which gascompressed in the chamber 17 can escape into the open. The free passagecross-section between the piston 15 and cylinder wall in the portion 21and the passage cross-section of the throttle passage 24 are expedientlyadapted to one another such that the counter-pressure in the chamber 17brings the upward movement of the piston to a standstill immediatelybefore it impacts against the upper wall of the cylinder 7. The throttlepassage 24, which is shown here as an opening spaced apart from thepiston rod 18 in the upper wall of the cylinder, may, of course, also beformed by a gap between the piston rod 18 and the upper wall of thecylinder surrounding it.

In FIGS. 3 and 4, the central portion 21 is shown cylindrically, with aslightly enlarged diameter compared to the portions 20, 22. Obviously,the inside width in the portion 21 could also be enlarged only on a partof its periphery, for example by one or more grooves extending in thedirection of the hollow axis of the cylinder 7 over the length of theportion 21, between which extend wall portions which are flush with theportions 20, 22 and also precisely guide the piston 15 in the centralportion 21.

A further-developed configuration of the actuator is explained with theaid of FIGS. 5 to 9. The cylinder 7 has substantially the sameconfiguration as that considered above. The piston 15 is subdivided intoa flat cylindrical central piece 25 rigidly connected to the piston rod18 and a sleeve 26 surrounding the central piece 25. The sleeve 26 has,at its upper and lower end, an inwardly directed peripheral web 27, ineach case, which forms a stop for the central piece 25. A plurality ofthrough openings 28 is formed at a distance from the upper edge of thesleeve 26, which is not greater than the thickness of the central piece25. A lower portion 29 of the sleeve 26 which is free of openings is atleast as long as the central portion 21 of the cylinder 7.

If the central piece 25 of the piston is driven out of the normalposition shown in FIG. 5 by propellant gas flowing in by way of the gasline 19, it firstly rises inside the sleeve 26, which, due to inertia,remains at rest. Only when the central piece 25 strikes against theupper web 27 is the sleeve 26 entrained and the piston 15 reaches theposition shown in FIG. 6, in which a passage of gas out of the lowerchamber 16 into the upper chamber 17 takes place by way of the throughopenings 28.

In the course of the further upward movement of the piston, as shown inFIG. 7, the latter is gradually decelerated by gas pressure building upin the upper chamber 17. In the position in which the piston comes torest, the openings have passed the portion 21, so no further gas canpass through them.

If a downward movement of the bonnet then starts under the pressure ofan impacting passenger, initially only the central piece 25 moves; thesleeve 26 only follows as soon as the central piece 25 has reached thelower web 27 of the sleeve 26, as shown in FIG. 8. Although the centralpiece 25 is now in the portion 21 of the cylinder 7, since the throughopenings 28 have remained in the portion 22, propellant gas cannot passto a significant extent from the lower chamber 16 into the upper chamber17, so that to force the piston down work has to be carried out which istaken from the impact energy of the pedestrian.

FIG. 9 shows the stage of downward movement of the piston in which thethrough openings 28 reach the central portion 21 of the cylinder. Atthis instant, the central piece 25 and the lower edge of the sleeve 26have already reached the portion 21, so no gas can overflow into theupper chamber 17 here either. Thus the pedestrian is effectivelydecelerated over the entire stroke of the piston 15 and optimallyprotected.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment, it being understood that variouschanges may be made in the function and arrangement of elementsdescribed in an exemplary embodiment without departing from the scope ofthe invention as set forth in the appended claims and their legalequivalents.

LIST OF REFERENCE NUMERALS

-   engine bonnet 1-   edge 2-   actuator 3-   edge 4-   actuator 5-   body part 6-   cylinder 7-   fastening flange 8-   gas inlet flange 9-   inlet opening 10-   gas generator carrier 11-   gas generator 12-   cover 13-   signal cable 14-   piston 15-   lower chamber 16-   upper chamber 17-   piston rod 18-   gas line 19-   portion 20, 21, 22-   arrow 23-   throttle passage 24-   central piece 25-   sleeve 26-   web 27-   opening 28-   portion 29-   upper wall 30

The invention claimed is:
 1. A pyrotechnic actuator, comprising: acylinder having a first chamber and a second chamber that are separatedby a central region; a piston that is configured to be displaced, underthe influence of a propellant gas, through the central region between afirst position in the first chamber and a second position in the secondchamber, wherein the piston includes openings; a first gas generatorthat is configured to be ignited to generate propellant gas; and whereinthe first chamber is configured to be charged with the propellant gas todisplace the piston, and wherein the second chamber is configured to becharged with the propellant gas that passes from the first chamberthrough the openings.
 2. A pyrotechnic actuator, comprising: a cylinderhaving a first chamber and a second chamber that are separated by acentral region; a piston on either side of the cylinder that isconfigured to be displaced between a first position in the first chamberand a second position in the second chamber, wherein the pistoncomprises a central piece connected to a piston rod and an apronsurrounding the central piece and axially displaceable thereon; and afirst gas generator for producing a propellant gas, wherein both thefirst chamber and the second chamber are configured to be charged withthe propellant gas such that the piston is configured to move throughthe central region between the first position and the second position.3. The actuator according to claim 2, wherein the second chamber isconfigured to be charged with the propellant gas after the charging thefirst chamber.
 4. The actuator according to claim 2, wherein the secondchamber is configured to be charged with the propellant gas through thefirst chamber.
 5. The actuator according to claim 2, wherein an inletpassage for propellant gas into the second chamber is blocked when thepiston is in a rest position of the piston and is open when the pistonis deflected from the rest position.
 6. The actuator according to claim5, wherein the inlet passage is blocked when the piston is in an endposition opposite to the rest position.
 7. The actuator according toclaim 2, wherein the inside width of the cylinder in a central region ofthe cylinder is greater than in at least one of its end regions.
 8. Theactuator according to claim 2, wherein the axial displaceability of theapron against the central piece is limited in both directions by stops.9. The actuator according to claim 2, wherein the apron has the localthrough openings.
 10. The actuator according to claim 2, wherein thespacing of the through openings from one end of the apron is greaterthan the length of the central region.
 11. The actuator according toclaim 2, wherein the second chamber communicates with the surroundingsby means of a throttle point.
 12. A pyrotechnic actuator, comprising: acylinder having a first chamber and a second chamber that are separatedby a central region and that are both configured to be charged by apropellant gas; a piston on either side of the cylinder that isconfigured to be displaced between a first position in the first chamberand a second position in the second chamber, wherein the piston includesopenings; and a first gas generator for producing a propellant gas,wherein both the first chamber and the second chamber are configured tobe charged with the propellant gas such that the piston is configured tomove through the central region between the first position and thesecond position, and wherein the second chamber is configured to becharged with the propellant gas that passes from the first chamberthrough the openings.
 13. A pyrotechnic actuator, comprising: a cylinderhaving a first chamber and a second chamber; a piston on either side ofthe cylinder that is configured to be displaced in the cylinder underthe influence of the propellant gas, wherein the piston comprises acentral piece connected to a piston rod and an apron surrounding thecentral piece and axially displaceable thereon; and a first gasgenerator for producing a propellant gas, wherein both the first chamberand the second chamber are configured to be charged with the propellantgas.
 14. The actuator according to claim 1, further comprising: a secondgas generator that is configured to be ignited independently of thefirst gas generator to generate propellant gas after the first gasgenerator has generated propellant gas.
 15. The actuator according toclaim 14, wherein the cylinder further comprises a flange with an inletopening, and further comprising: a carrier that is fastened to theflange of cylinder and that comprises chambers for holding the first andsecond gas generators, and wherein each of the first and second gasgenerators is coupled to the inlet opening to provide propellant gas tothe cylinder.
 16. The actuator according to claim 14, furthercomprising: an electronic ignition circuit that is configured to ignitethe first and second gas generators individually and sequentially inresponse to external ignition commands.